1. Field of the Invention
The present invention relates to a communication apparatus, a power supply control method, a computer program product for power supply control, a display apparatus, a communication method, and a computer program product for communication, for realizing a function of sharing a screen of an application between apparatuses.
2. Description of the Related Art
To improve usability, computing systems have been offered, in which a terminal having a minimum input/output interface is arranged on a user's side, while complicating calculating processes are executed on a machine that is arranged at a remote location. For example, U.S. Pat. No. 6,784,855 and JP-A 2002-323942 (KOKAI) disclose technologies of systems in which the screen information of a communication apparatus (such as a personal computer and a server computer) is displayed on a remote display apparatus (display terminal) on a network.
In such a system, information input from the display terminal (e.g. information input with a stylus pen of a digitizer) is transmitted to the communication apparatus so that the actual process of an application program is executed by the communication apparatus on the network. Then, execution results and screen update information are transmitted to the display apparatus. The display terminal executes a drawing process, based on the received screen update information.
Meanwhile, a technology called Wake on LAN (WOL) has been offered, with which a computer connected to a local area network (LAN) is activated by a remote computer on the network. With the WOL technology applied to the above computing system, the user is allowed to control the main power supply of the communication apparatus remotely from the display apparatus, without directly operating the main switch of the communication apparatus.
The communication apparatus activated by the WOL can return to the power-off state by setting a timer on the side of the communication apparatus and turning the power off when no input operation is performed for a certain period of time. For example, JP-A 2002-323942 (KOKAI) teaches a display terminal technology of shifting to a power-saving saving mode when no input is performed for a certain period of time.
With the method of shutting off the power when the function of the communication apparatus is not in use for a predetermined period of time, the power is not always turned off appropriately. For example, the judgment as to whether the function of the communication apparatus is not in use for a predetermined period of time may be made with a method of detecting that the communications between the display terminal and the communication apparatus are disconnected.
Communications could be disconnected for different reasons, however. The reasons may be: (1) that the user turns the power of the display terminal off; (2) that wireless communications are in poor condition, and are temporarily disconnected; (3) that the operation mode of the display terminal is changed when the display terminal makes an access to data resources stored in the communication apparatus such as video data, music data, and photograph data and reproduces the data through streaming; and (4) that the operation mode is changed when the display terminal reproduces media data stored in its own memory device.
In the situations of (1) and (4), no problem arises when the communication apparatus is turned off. However, in the situations of (2) and (3), communications should be reestablished with the communication apparatus, and thus the communication apparatus should not be turned off. Once it is turned off, the WOL start-up procedure needs to be conducted from the beginning to reconnect the display terminal to the communication apparatus, which would lower the usability.
However, when the communications are disconnected, it is impossible for the communication apparatus to judge the cause of the disconnection and determine whether the display terminal wants to be reconnected. Thus, it has been difficult to turn the power off exclusively when the display terminal is not actually using data resources or processing functions of the communication apparatus.
To reduce the possibilities of turning the power off in the situations of (2) and (3), the standby time before switching to the shut-down or power-saving mode could be set longer. This would raise a problem of wasting power, however, because the communication apparatus cannot be turned off for a predetermined period of time even if the display apparatus does not at all use the data resources or processing functions of the communication apparatus.